Led packages and related methods

ABSTRACT

An LED package with trenches traversing a die pad to provide a mechanical interlock mechanism to strengthen bonding between the die pad and an insulator such that de-lamination is less likely to occur between the die pad and the insulator. A chip carrying region is defined by a barrier portion formed by the insulator in the trenches and in gaps between electrodes and the die pad, such that a light converting layer is confined within the barrier portion.

TECHNICAL FIELD

The present invention relates to a package structure, and in particularto a light-emitting diode package structure.

BACKGROUND

Light-emitting diode (LED) devices have many diverse applications. Forexample, they are used as light sources for scanners, projectors, liquidcrystal displays, fascias, traffic lights, etc. Compared withconventional light sources, such as incandescent lights, LED deviceshave numerous advantages, including compact size, long lifespan, lowdriving voltage/current, high structural strength, no mercury content(so less pollution when disposed of), high luminous efficiency forenergy savings, etc.

LED devices typically include at least one surface-mount type LEDpackage with an LED chip therein. LED packages including a pre-moldedlead frame to carry the LED chip, instead of a conventional ceramicsubstrate, have been proposed. A pre-molded lead frame includes aninsulating molding material encapsulating a lead frame having positiveand negative electrical contacts exposed from the molding material.

Unfortunately, the bond between the lead frame and the molding materialtends to be relatively weak, and the difference between the coefficientsof thermal expansion (CTE) the lead frame and the molding material isvery large. Because of the CTE mismatch, stresses are induced at theinterface between the lead frame and the molding material as theconventional package experiences temperature cycling. The stresses, inturn, result in the delamination between the lead frame and the moldingmaterial when, for example, the LED package is surface-mounted to aprinted wiring board during A solder reflow process. The LED package maysubsequently be damaged by exposure to air or moisture through thedelamination site.

SUMMARY

One of the present embodiments comprises a light-emitting diode (LED)package. The package comprises a housing having an opening with an opentop, a closed bottom and side walls extending between the closed bottomand the open top. The housing includes a lead frame including a die padand at least one electrode. The at least one electrode is isolated fromthe die pad by at least one gap. The die pad includes first and secondtrenches located within the opening of the housing. An end of eachtrench is connected to the at least one gap. The housing furtherincludes a first insulator partially encapsulating the lead frame suchthat a portion of the upper surface of the die pad and a portion of theat least one electrode are exposed from the first insulator and the atleast one gap and the trenches are at least partially filled by thefirst insulator. The package further comprises an LED chip disposed onthe exposed upper surface of the die pad and located between the twotrenches. The package further comprises at least one wire connecting theLED chip to the exposed part of the at least one electrode. The packagefurther comprises a second insulator encapsulating the LED chip and thewire.

Another of the present embodiments comprises a carrier for alight-emitting diode (LED) package. The carrier comprises a lead frame.The lead frame includes a die pad having an upper surface, a lowersurface, and first and second trenches extending completely across theupper surface. The lead frame further includes first and secondelectrodes located on opposite sides of the die pad and being isolatedtherefrom. The die pad and the first electrode are separated by a firstgap that connects a first end of the first trench and a first end of thesecond trench. The die pad and the second electrode are separated by asecond gap that connects a second end of the first trench and a secondend of the second trench. The upper surface of the die pad comprises achip carrying region bounded by the first gap, the second gap, the firsttrench, and the second trench. The carrier further comprises aninsulator encapsulating a portion of the lead frame. The insulatorleaves exposed at least the chip carrying region of the die pad, aportion of the first electrode, and a portion of the second electrode.The first and second gaps and the first and second trenches are at leastpartially filled by the insulator.

Another of the present embodiments comprises a light-emitting diode(LED) package. The package comprises a lead frame. The lead frameincludes a die pad having first and second trenches traversing an uppersurface thereof. The lead frame further includes first and secondelectrodes located on opposite sides of the die pad and spaced therefromby first and second gaps connecting the first and second trenches. Thegaps and the trenches define a chip carrying region on the die pad. Thepackage further comprises a first insulator at least partially fillingthe first and second trenches and the first and second gaps and forminga barrier portion surrounding the chip carrying region. The packagefurther comprises an LED chip located in the chip carrying region. Thepackage further comprises a plurality of wires connecting the LED chipto the first and second electrodes. The package further comprises asecond insulator encapsulating the LED chip and the wires.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of one embodiment of an LED package;

FIG. 2 is a side cross-sectional view of the LED package of FIG. 1 takenalong the line 2-2 in FIG. 1;

FIG. 3 is a top perspective view of a lead frame of the LED package ofFIG. 1;

FIG. 4 is a bottom perspective view of the lead frame of FIG. 3;

FIG. 5 is a top plan view of the LED package of FIG. 1;

FIG. 6 is a top plan view of another embodiment of an LED package;

FIG. 7 is a partial side cross-sectional view of the LED package of FIG.2;

FIG. 8 is a partial side cross-sectional view of another embodiment ofan LED package;

FIG. 8A is a top perspective view of the LED package of FIG. 8;

FIG. 9 is a partial side cross-sectional view of another embodiment ofan LED package;

FIG. 10 is a partial side cross-sectional view of another embodiment ofan LED package;

FIG. 11 is a top perspective view of another embodiment of a lead framefor an LED package;

FIG. 12 is a top plan view of another embodiment of an LED package;

FIG. 13 is a top perspective view of the LED package of FIG. 12; and

FIGS. 14-16 are side elevation views of three other embodiments of LEDpackages.

Common reference numerals are used throughout the drawings and thedetailed description to indicate the same elements. The presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

Referring to FIG. 1, an LED package 100 according to one of the presentembodiments is shown. The LED package 100 includes a housing 102including a lead frame 110 encapsulated in a first insulator 120, an LEDchip 130 disposed in an opening defined within the housing 102, and asecond insulator, or lens, 150.

Referring to FIG. 2, which is a side cross-sectional view of the LEDpackage 100 if FIG. 1, the lead frame 110 includes a die pad 112, afirst electrode 114, and a second electrode 116. The lead frame 110 istypically made of metal, such as copper or aluminum. The surface of thelead frame 110 may be plated with a metal coating, such as silver orgold. to enhance conductivity.

The first electrode 114 and the second electrode 116 are located onopposite sides of the die pad 112. The die pad 112 and the firstelectrode 114 are separated by a first gap 170, and the die pad 112 andthe second electrode 116 are separated by a second gap 180. Referring toFIG. 3, which illustrates the lead frame 110 from an upper perspective,the die pad 112 includes two trenches 117 a, 117 b traversing the uppersurface 112 a thereof. In an alternative embodiment, the two trenchesmay extend only partially across the upper surface 112 a, as illustratedby trenches 118 a and 118 b in FIG. 6, which is discussed in detailbelow.

Referring back to FIGS. 2 and 3, the first gap 170 separates the die pad112 from the second electrode 116, and the second gap 180 separates thedie pad 112 from the first electrode 114. Thus, on the upper surface 112a of the die pad 112, the first gap 170, the second gap 180, the firsttrench 117 a, and the second trench 117 b define boundaries of a chipcarrying region 112 b. The trenches 117 a, 117 b are filled by a part ofthe first insulator 120. Since the trenches 117 a, 117 b are locatedwithin the housing's opening, the insulator 120 filling the trenches 117a, 117 b provides additional mechanical interlock to strengthen thebonding between the die pad 112 and the first insulator 120, such thatdelamination does not easily occur between the die pad 112 and the firstinsulator 120. Referring to FIG. 4, which illustrates the lead frame 110from a lower perspective, the lead frame 110 includes at least oneconcave portion 115 on the first electrode 114 or the second electrode116.

Referring to FIG. 2. and as further described below, the first insulator120 extends around portions of the lead frame 110 to electricallyisolate the die pad 112, the first electrode 114, and the secondelectrode 116 from one another. The first insulator 120 further forms aperimeter portion 124 that circumscribes the package 100, and is definedby a vertical outer wall 124 a and a slanted inner wall 190. The slantedinner wall 190 is circular to accommodate the hemispherical secondinsulator 150. The perimeter portion 124 and the lead frame 110 togetherdefine a housing including an opening with an open top, a closed bottomand sides 190 connecting the closed bottom and the open top. In certainembodiments, the first insulator 120 may be a molding compound, such as,for example, a transparent polymer or a translucent polymer, a soft gel,an elastomer, a resin, an epoxy resin, a silicone, and/or anepoxy-silicone hybrid resin.

Referring to FIG. 5, at least a portion of the die pad 112, a portion ofthe first electrode 114, and a portion of the second electrode 116 areexposed from the first insulator 120 at the closed bottom of the housing(the exposed portions are illustrated by hatched lines). Moreover, thefirst gap 170 and the second gap 180 are filled with the first insulator120 so that the die pad 112 is electrically insulated from the firstelectrode 114 and the second electrode 116.

With continued reference to FIG. 5, the LED chip 130 is disposed on theupper surface 112 a of the die pad 112 in a manner that provides forgood heat conduction between the LED chip 130 and the die pad 112. Forexample, the LED chip 130 can be secured to the upper surface 112 a bymetal soldering. Wires 140 connect the exposed portion of the firstelectrode 114 or the second electrode 116 to electrical contacts (e.g.,anode and cathode contacts) of the LED chip. In alternative embodimentswhere the cathode contact is not disposed on the upper side of the chip130, as in the illustrated embodiment, but is instead on its lower side,it can be electrically connected with the die pad 112 with anelectrically conducting material, and one of the electrodes 114, 116 maybe omitted.

With continued reference to FIG. 5, the inner side wall of the perimeterportion 124 includes a first notch 192 and a second notch 194 formed atlocations corresponding to a first wire bonding region 114 a of thefirst electrode 114 and a second wire bonding region 116 a of the secondelectrode 116, respectively. In alternative embodiments, the notches192, 194 may be omitted if the wire bonding operation does not requirethe extra exposed area provided by the notches 192, 194.

With reference back to FIGS. 1 and 2, the second insulator 150encapsulates the LED chip 130 and the wires 140. In certain embodiments,the second insulator 150 may be a molding compound, such as, forexample, a transparent polymer or a translucent polymer, a soft gel, anelastomer. a resin, an epoxy resin, a silicone, and/or an epoxy-siliconehybrid resin. To improve the uniformity of light emitted by the LEDpackage described above, it may be desirable to scatter the light as itemits from the various emitters. For example, adding scatteringparticles (not shown) to the second insulator 150 will randomly refractthe light.

With reference to FIG. 2, the light converting layer 160 is disposedbetween the second insulator 150 and the LED chip 130, and covers theLED chip 130 and portions of the wires 140 (not shown in FIG. 2). Thelight converting layer 160 includes particles of a light convertingsubstance (not shown), for example, fluorescent particles. Light, forexample, blue light, emitted from the LED chip 130 may be converted bythe light converting substance into light of different colors, forexample, green, yellow, or red, and the lights of different colors aremixed to generate white light. The light converting layer 160 isoptional. For example, the light converting layer 160 may not berequired in a monochromatic LED package. In another embodiment, thelight converting layer 160 may also be replaced by adding the lightconverting substance into the second insulator 150.

With continued reference to FIG. 2, the LED package 100 further includesa protection device 132 that protects the chip 130 from excessivecurrent. The protection device 132 is disposed on the second electrode116 and is electrically connected to the first electrode 114 through awire (not shown). The first insulator 120 covers the protection element132.

The protection device 132 may be, for example, a Zener diode. Zenerdiodes can adjust working voltage and stabilize circuits.

With reference to FIG. 7, which is a partial side cross-sectional viewof the LED package of FIG. 2 with the perimeter portion 124 and secondinsulator 150 omitted for clarity, a portion of the first insulator 120located in the first gap 170, the second gap 180, the first trench 117a, and the second trench 117 b forms a barrier portion 122 surroundingthe chip carrying region 112 b. The barrier portion 122 has an uppersurface 122 a substantially coplanar with the upper surface 112 a of thedie pad 112. In one embodiment, the light converting layer 160 is fowledfrom a light converting composition including phosphor particles andsilica particles dispersed in an optically clear silicone polymer, whichcan be cured by heat or light. The light converting composition, in aliquid state. may be dispensed onto the chip 130 and the upper surface112 a of the die pad 112 adjacent to the chip 130, and then cured to asolid state, thereby fowling the light converting layer 160. Since thematerial properties of the light converting composition enable it tobetter adhere to the metallic die pad 112 than to the organic barrierportion 122. the light converting composition can be confined within thebarrier portion 122 and, once cured to a solid state, the resultinglight converting layer 160 is confined within the barrier portion 122.

Another embodiment is illustrated in FIGS. 8 and 8A, where FIG. 8A is atop perspective view of the LED package of FIG. 8 with the chip 130 andthe light converting layer 160 omitted for clarity. The barrier portion622 has an upper surface 622 a that is elevated above the upper surface112 a of the die pad 112. The barrier portion 622 thus confines thelight converting layer 160 to the area within the barrier portion 622.In still another embodiment, illustrated in FIG. 9, the barrier portion722 has an upper surface 722 a that is elevated above the upper surface112 a of the die pad 112, and a bevel 122 b on a side thereof facing theLED chip 130. This configuration of the barrier portion 722 confines thelight converting layer 160 to the area within the barrier portion 722and increases the light-emitting efficiency. In still anotherembodiment, illustrated in FIG. 10, the barrier portion 822 has an uppersurface 822 a that is recessed below the upper surface 112 a of the diepad 112, and is concave. This configuration of the barrier portion 822confines the light converting layer 160 to the area within the barrierportion 822 via the concave profile of the upper surface 822 a. Thelight converting layer 160 confined within the barrier portions 622,722, 822 of the embodiments of FIGS. 8-10 is preferably cured to befirmly attached to the upper surface 112 a of the die pad 112.

With reference to FIG. 11, a lead frame 110 a according to another ofthe present embodiments includes one or more concave portions 113 a onthe upper surface 112 a of the die pad 112. The concave portions 113 aare configured to be filled by the first insulator 120, so as toincrease the bonding strength between the die pad 112 and the firstinsulator 120. thereby reducing the likelihood of de-lamination betweenthe die pad 112 and the first insulator 120. Similarly, the lead frame110 a includes at least one concave portion 115 on a surface of thefirst electrode 114 and/or the second electrode 116 configured for thesame purpose.

With reference to FIGS. 12 and 13, in the illustrated embodiment thefirst insulator 120 covers the entire upper surface of the lead frame110 except the first wire bonding region 114 a, the second wire bondingregion 116 a, and the chip carrying region 112 b. In other words, onlythe first wire bonding region 114 a, the second wire bonding region 116a, and the chip carrying region 112 b of the lead frame 110 are exposedfrom the first insulator 120.

FIGS. 14-16 illustrate side elevation view of several LED packageshaving different configurations for the second insulator 150. Withreference to FIG. 13, a top surface of the second insulator is coplanarwith the top surface of the perimeter portion 124. With reference toFIG. 15, the second insulator 150 includes a dome-shaped lens portionthat increases the light emitting efficiency of the LED packagestructure 100. With reference to FIG. 16, the second insulator 150includes a lens portion shaped like an ellipsoid with the top portiontruncated to form a substantially flat surface.

While the invention has been described and illustrated with reference tospecific embodiments thereof, these descriptions and illustrations donot limit the invention. It should be understood by those skilled in theart that various changes may be made and equivalents may be substitutedwithout departing from the true spirit and scope of the invention asdefined by the appended claims. The illustrations may not necessarily bedrawn to scale. There may be distinctions between the artisticrenditions in the present disclosure and the actual apparatus due tomanufacturing processes and tolerances. There may be other embodimentsof the present invention which are not specifically illustrated. Thespecification and the drawings are to be regarded as illustrative ratherthan restrictive. Modifications may be made to adapt a particularsituation, material, composition of matter, method, or process to theobjective, spirit and scope of the invention. All such modifications areintended to be within the scope of the claims appended hereto. While themethods disclosed herein have been described with reference toparticular operations performed in a particular order, it will beunderstood that these operations may be combined, sub-divided, orre-ordered to form an equivalent method without departing from theteachings of the invention. Accordingly, unless specifically indicatedherein, the order and grouping of the operations are not limitations ofthe invention.

What is claimed is:
 1. A light-emitting diode (LED) package, comprising:a housing having an opening with an open top, a closed bottom and sidewalls extending between the closed bottom and the open top, the housingincluding a lead frame including a die pad and at least one electrode,the at least one electrode being isolated from the die pad by at leastone gap, the die pad including first and second trenches located withinthe opening of the housing, an end of each trench being connected to theat least one gap; a first insulator partially encapsulating the leadframe such that a portion of the upper surface of the die pad and aportion of the at least one electrode are exposed from the firstinsulator and the at least one gap and the trenches are at leastpartially filled by the first insulator; an LED chip disposed on theexposed upper surface of the die pad and located between the twotrenches; at least one wire connecting the LED chip to the exposed partof the at least one electrode; and a second insulator encapsulating theLED chip and the wire.
 2. The LED package of claim
 1. further comprisinga light converting layer disposed between the second insulator and theLED chip and covering the LED chip.
 3. The LED package of claim 2,wherein the portions of the first insulator in the gap and the firsttrenches form a barrier portion surrounding the light converting layer.4. The LED package of claim 3, wherein an upper surface of the barrierportion is elevated above the upper surface of the die pad, and a sideof the upper surface of the barrier portion facing the LED chip isbeveled.
 5. The LED package of claim 3, wherein an upper surface of thebarrier portion is substantially coplanar with the upper surface of thedie pad.
 6. The LED package of claim 3, wherein an upper surface of thebarrier portion is recessed below the upper surface of the die pad. 7.The LED package of claim 1, wherein the at least one electrode comprisesat least one concave portion that is at least partially filled by thefirst insulator.
 8. The LED package of claim 1, wherein the uppersurface of the die pad comprises at least one concave portion that is atleast partially filled by the first insulator.
 9. The LED package ofclaim 1, wherein the first insulator comprises a wall portionsurrounding the chip, the wall portion and the lead frame togetherforming a concave cup structure, and the exposed portion of the uppersurface of the die pad and the exposed portions of the electrodes arelocated on a bottom of the concave cup structure.
 10. The LED package ofclaim 9, wherein a side wall of the wall portion of the concave cupstructure comprises a notch exposing a wire bonding region of theelectrode.
 11. The LED package of claim 10, wherein the first insulatorcovers all regions of the lead frame on the same side as the uppersurface except the first wire bonding region. the second wire bondingregion, and a chip carrying region defined by the at least one gap andthe first and second trenches.
 12. A carrier for a light-emitting diode(LED) package, the carrier comprising: a lead frame, including a die padhaving an upper surface, a lower surface, and first and second trenchesextending completely across the upper surface: first and secondelectrodes located on opposite sides of the die pad and being isolatedtherefrom, the die pad and the first electrode being separated by afirst gap that connects a first end of the first trench and a first endof the second trench, the die pad and the second electrode beingseparated by a second gap that connects a second end of the first trenchand a second end of the second trench, the upper surface of the die padcomprising a chip carrying region bounded by the first gap, the secondgap, the first trench, and the second trench; and an insulatorencapsulating a portion of the lead frame, wherein the insulator leavesexposed at least the chip carrying region of the die pad, a portion ofthe first electrode, and a portion of the second electrode, and whereinthe first and second gaps and the first and second trenches are at leastpartially filled by the insulator.
 13. The carrier of claim 12, whereinthe portion of the insulator in the first and second gaps and the firstand second trenches forms a barrier portion surrounding the chipcarrying region, an upper surface of the barrier portion is elevatedabove the upper surface of the die pad, and the light converting layeris surrounded by the barrier portion.
 14. The carrier of claim 13.wherein a side of the upper surface of the barrier portion is beveled.15. The carrier of claim 12, wherein the portion of the insulator in thefirst and second gaps and the first and second trenches forms a barrierportion surrounding the chip carrying region, an upper surface of thebarrier portion is substantially coplanar with the upper surface of thedie pad, and the light converting layer is surrounded by the barrierportion.
 16. The carrier of claim 12, wherein the portion of theinsulator in the first and second gaps and the first and second trenchesforms a barrier portion surrounding the chip carrying region, an uppersurface of the barrier portion is recessed below the upper surface ofthe die pad, and the light converting layer is surrounded by the barrierportion.
 17. The carrier of claim 12, wherein the insulator comprises awall portion located on a periphery of the lead frame and surroundingthe chip carrying region, the wall portion and the lead frame togetherform a concave cup structure, and the chip carrying region is located ona bottom of the concave cup structure.
 18. The carrier of claim 17,wherein a side wall of the wall portion of the concave cup structurecomprises a first and second notches that expose a first wire bondingregion of the first electrode and a second wire bonding region of thesecond electrode.
 19. A light-emitting diode (LED) package, comprising:a lead frame including a die pad having first and second trenchestraversing an upper surface thereof; first and second electrodes locatedon opposite sides of the die pad and spaced therefrom by first andsecond gaps connecting the first and second trenches, the gaps and thetrenches defining a chip carrying region on the die pad; a firstinsulator at least partially filling the first and second trenches andthe first and second gaps and forming a barrier portion surrounding thechip carrying region; an LED chip located in the chip carrying region; aplurality of wires connecting the LED chip to the first and secondelectrodes; and a second insulator encapsulating the LED chip and thewires.
 20. The LED package of claim 19, wherein an upper surface of thebarrier portion is elevated above, substantially coplanar with, orrecessed below the upper surface of the die pad, and the lightconverting layer is surrounded by the barrier portion.